Semiconductor memory device with multiple registers enabling serial output

ABSTRACT

A semiconductor memory device having a memory cell array (MCA) composed of a plurality of memory cells arranged in a matrix pattern including a plurality of columns, a data register section provided with two first and second registers each having &#34;a&#34;-units of one-bit data register; a control section for selecting two sets of &#34;a&#34;-units of the column from a plurality of the columns for each &#34;a&#34;-cycles in accordance with inputted and read addresses, and for storing the &#34;a&#34; units of data of the selected 2 &#34;a&#34;-units of column in either one of the first and second registers alternately on the basis of a sequence of the read addresses; and a data output section for scanning and outputting data of the 2 &#34;a&#34;-units of the one-bit data register in sequence. Data of column bits more than the number of the registers can be accessed continuously in spite of the minimum register configuration. Further, the head column address can be selected freely.

FIELD OF THE INVENTION

The present invention relates to a semiconductor memory device, and more specifically to a semiconductor memory device suitable for a clock-synchronous random access memory which can output data at high speed and at random.

BACKGROUND OF THE INVENTION

With the recent advances of higher processing speed, a microprocessor is provided with a primary memory device with a large capacity. To obtain the large capacity primary memory device, there has been proposed a memory device capable of accessing data at high speed at the sacrifice of random characteristics of data access, in order to solve a bottleneck with respect to low processing speed due to the low access speed of the external memory device.

An example of the memory device as described above has been proposed (not yet published) by the present inventor in Japanese Patent Application No. 3-255354, in which an address is acquired within a predetermined number of cycles of a basic clock supplied to the system and further data input and output starts a predetermined cycles after the cycle at which the address is acquired. In addition, Japanese Patent Application No. 4-638135 (not yet published) discloses a memory device provided with internal data registers, which operates as follows: a group of access data are stored in the internal registers temporarily for data access between the outside and the memory cells. The data to be stored in the registers are selected by scrambler circuits; that is, a scrambler control circuit controls the scrambler circuits so that access data can be stored cyclically in the respective registers at predetermined sequence for each cycle of a clock signal. Further, the data are inputted and outputted between the outside and the registers via an input/output buffer. In response to a head address indicative of data access start, a predetermined selection sequence of the scrambler circuits is determined.

The above-mentioned semiconductor memory device will be described in more detail with reference to FIG. 4. In FIG. 4, a column decoder 1 selects one of cell blocks CB1 to CB5 of a memory core 2. Each of the cell blocks CB1 to CB5 includes 4 columns CM1 to CM4. Data stored in the four columns CM1 to CM4 of one of the cell blocks CB1 to CB5 (selected by the column decoder 1) are outputted to data lines DLN simultaneously. The data on the data lines DLN are transferred to read/write data lines RWD via a data buffer 4. The read/write data lines RWD are connected to data registers 51 and 52 via scrambler circuits 61 and 62, respectively. A scrambler control circuit 7 controls the two scrambler circuits 61 and 62 so that the data on the read/write data line RWD can be selectively stored 2 bits by 2 bits in data areas R1, R2, R3 and R4 of the data registers 51 and 52, respectively. The data stored in the data registers 51 and 52 are selected by a data selection section 9 and then outputted through a data output buffer 8 as data output.

The operation of the memory device as shown in FIG. 4 will be described hereinbelow.

One block of the five cell blocks CB1 to CB5 of the memory cell 2 is selected by the column decoder 1. Data of the four columns CM1 to CM4 of the selected block are read simultaneously to the data lines DLN, and then transferred to the read/write data lines RWD via the data buffer 4. The four bit data are selectively stored 2 bits by 2 bits in the data areas R1, R2, R3 and R4 of the data registers 51 and 52, respectively via the scrambler circuits 61 and 62 controlled by the scrambler control circuit 7. For instance, the access sequence of the data areas R1, R2, R3 and R4 of the data registers 51 and 52 is as follows: R1, R2, R3 and R4. The data stored in the data areas R1, R2, R3 and R4 are selected by the data selector section 9, transferred to the data output buffer 8, and then outputted therefrom as the data output.

In the semiconductor memory device as described above, however, there exists a problem in that it is impossible to start data access beginning from any given bit of the columns CM1 to CM4, when data more than 4 bits (the number of data areas) are required to be outputted from the data areas R1, R2, R3 and R4 of the data registers 51 and 52. The reason is as follows: since the columns CM1 to CM 4 selected by the column decoder 1 are fixed, when 8-bit data are accessed, it is impossible to constitute 8-bit data by simply combining 2 sets of 4-bit data. In other words, it is impossible to obtain an 8-bit continuous access. For example, if the access sequence as "3"-"4"-"5"-"6"-"7"-"8"-"1"-"2" is required, the access sequence is inevitably determined as "3"-"4"-"1"-"2"-"5"-" 6"-"7"-"8" or "3"-"4"-"1"-"2"-"7"-"8"-"5"-"6". Although this problem can be solved by using more larger-scale registers or by sacrificing the access speed, this method raises another problem in that the memory characteristics of the synchronous memory device are deteriorated.

SUMMARY OF THE INVENTION

With these problems in mind, therefore, the object of the present invention is to provide a clock-synchronous semiconductor memory device high in access speed, by which data of column bits more than the number of registers can be accessed continuously, in spite of the minimum number of registers, and further the column address from which the access starts can be selected freely.

To achieve the above-mentioned object, the present invention provides a semiconductor memory device, comprising: a memory cell array composed of a plurality of memory cells arranged roughly in a matrix pattern including a plurality of columns; data register means provided with two first and second registers each having "a"-units of one-bit data register; control means for selecting two sets of "a"-units of the column from a plurality of the columns for each a-cycles in accordance with inputted and read addresses, and for storing the "a"-units of data of the selected 2 "a"-units of column in either one of the first and second registers alternately on the basis of a sequence of the read addresses; and data output means for scanning and outputting data of the 2 "a"-units of the one-bit data register in sequence.

The data output means outputs data in synchronism with a clock inputted from the outside. The "a"-units of the column forms one column group in said memory cell array. The control means comprises a plurality of column select lines each for selecting one column group. The columns are connected to the one-bit data registers, respectively through a data transfer line. The data transfer line includes 2 "a"-units of data transfer line.

The control means executes such a first control operation, in response to a head column address for data output, that 2 "a"-units of data on 2 "a"-units of the column are transferred to 2 "a"-units of the data transfer lines, by activating the column select lines for selecting the column address group including a column corresponding to the head column address and further the column select lines for selecting the column group including columns corresponding to the column addresses selected successively in sequence. Further, the control means executes such a second control operation that any given column data are outputted as head data for each a-cycles, by selecting "a"-units of data from the 2 "a"-units of data onto 2 "a"-units of the data transfer lines, by storing the selected data in "a"-units of the one-bit data register of the registers, to which data are not stored in the preceding data transfer operation, in output sequence, and by repeating the above-mentioned operation.

In accordance with the read address, the control means selectively turns on two predetermined groups of column gate groups to transfer 2 "a"-unit data to the data line groups. Further, "a"-unit data (based on the read address) of 2 "a"-unit data are stored in the "a"-unit registers of the first data register group in sequence of the data read operation under control of the control means. The same operation is applied to the second data register group. The above-mentioned operation is repeated to output the data from the respective columns in read address sequence.

In the semiconductor memory device according to the present invention, column data more than the number of the data registers arranged on the output side can be accessed continuously, irrespective of the number of the data registers directly, and further any access start address can be determined.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is block diagram showing one embodiment of the semiconductor memory device according to the present invention;

FIG. 2 is a timing chart for assistance in explaining the operation of the memory device shown in FIG. 1;

FIG. 3 is a block diagram showing another embodiment of the semiconductor memory device according to the present invention; and

FIG. 4 is a block diagram showing a semiconductor memory device disclosed in a prior application by the present inventor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present invention will be described hereinbelow with reference to the attached drawings.

FIG. 1 is a block diagram showing one embodiment of the semiconductor memory device according to the present invention. In FIG. 1, a memory cell array MCA includes a plurality of memory cells arranged in matrix pattern. To the memory cell array MCA, decode signals are applied from a row decoder RD. As shown in FIG. 1, columns b11, b12, b21, b22, b31, b32, b41, b42, . . . , b(n/2)1, b(n/2)2 which constitute the memory cell array 1 have a pair of complementary bit lines, respectively. Data on the bit lines can be read by sensing the bit line data by sense amplifiers. The columns b11, b12, b21, b22, b31, b32, b41, b42, . . . , b(n/2)1, b(n/2)2 are connected to column gates 11, 12, 13, 14, 15, 16, 17, 18, . . . 1n-1, 1n, respectively. The column gates 11 to 1n are turned on or off by column select lines C1 to Cn/2, respectively. Two of the column select lines are selected by a column gate group selection circuit CGS. Two column gates are turned on by the single selected column select line. Data on the columns b11, b12, ..., b(n/2)1, b(n/2)2 are transmitted to data lines DLN through the column gates 11 to 1n. A scrambler control circuit 10 controls scrambler circuits 61 and 62, and further selects two column select lines C1 to Cn/2 through the column gate group selection circuit CGS. To the scrambler control circuit 10, a read address A_(READ) is applied.

The operation of the memory device thus constructed will be explained hereinbelow.

When the column select line C1 is activated, two data on the columns b11 and b12 are outputted to the data lines DLN through the column gates 11 and 12. In the same way, when the column select line C2 is activated, two data on the columns b21 and b22 are outputted to the data lines DLN through the column gates 13 and 14. In the same way, when the column select line Cn/2 is activated, two data on the columns b(n/2)1, b(n/2)2 are outputted to the data lines DLN through the column gates 1n-1 and 1n.

Here, two of the column select lines C1 to Cn/2 are activated simultaneously by the scrambler control circuit 10. As a result, four of the column gates 11 to 1n can be selected, so that 4-bit data are outputted from the four columns to the data lines DLN. In this case, the column select lines C1 to Cn/2 are selected in such a way that a plurality of the data are not outputted to the same data lines DLN for prevention of data interference. For instance, the column select lines C1 and C3 are not selected simultaneously.

The 4-bit data transferred to the data line DLN are amplified by the data buffer 4, and then transferred to the read/write data lines RWD. Two bits of each of the 4-bit data transferred to the read/write lines RWD as described above are selected by the scrambler circuits 61 and 62, respectively, and then stored in data areas R1 and R2 of a data register 51 or in data areas R3 and R4 of a data register 52, respectively under control of the scrambler control circuit 10 to the scrambler circuits 61 and 62. The data in the areas R1, R2, R3 and R4 of the data registers 51 and 52 are selected by a data selection section 9, and then outputted to the outside through a data output buffer 8 as data output.

FIG. 2 is a timing chart which shows the above-mentioned operation in sequence with respect to time. In FIG. 2, (A) indicates a basic clock CLK; (B) indicates a column address select signal /CAS; (C) indicates data including data to be stored in the data areas R1/R2, respectively; (D) indicates a timing at which data are stored in the data areas R1/R2, respectively; (E) indicates a timing at which data are stored in the data areas R3/R4, respectively; (F) indicates data including data to be stored in the data areas R3/R4, respectively; (G), (H) and (I) indicate the statuses of output 1, output 2 and output 3 derived as data output, respectively; and (J) indicates the statuses of the column select lines C1 to Cn/2 , respectively.

The selection of the column select lines C1 to Cn/2 are executed newly for each cycle "1", "3", "5", "7", . . . of the clock CLK. The data at the newly selected columns b11 to b(n/2 )2 develop on the read/write data lines RWD roughly after two cycles as deterministic data. FIGS. 2(C) and (F) show these deterministic data. Each of these data can be determined being transferred 4 bits by 4 bits. Two bits of the four bits are stored in the data registers 51 and 52, respectively. Therefore, in FIG. 2, data are shown for each data register 51 or 52. Here, FIG. 2(C) shows 4-bit data including 2-bit data to be stored in the data areas R1 and R2 of the data register 51. Further, FIG. 2(F) shows 4-bit data including 2-bit data to be stored in the data areas R3 and R4 of the data register 52. When these data have been stored in the data registers 51 and 52 at the time point at which having been determined, it is possible to output these data to the outside by accessing the data stored in the data areas R1, R2, R3 and R4 in sequence with the use of the data selection section 9. FIGS. 2(D) and (E) show the timings at which the data are stored in the data registers 51 and 52 under control of the scrambler control circuit 10. In more detail, when a data storing signal is at "H" level, data are held in the data areas R1, R2, R3 and R4 of the data registers 51 and 52. On the other hand, when a data storing signal is at "T" level, data of the 4-bit data on the read/write data lines RWD are stored in the data areas R1, R2, R3 and R4 of the data registers 51 and 52 in accordance with the selection of the scrambler circuits 61 and 62.

The data output 1 can be obtained from an address determined in response to the clock CLK "1" as follows: The column address select lines C1 to Cn/2 including the determined head address and the column address select lines C1 to Cn/2 adjacent thereto in the output sequence direction are selectively activated under control of the scrambler control circuit 10. Consequently, the corresponding column gates 11, 12, 13, . . . , 1n are selected, so that 4-bit data are outputted to the data lines DLN. These data are sensed by the data buffer 4 to determine the read/write data line RWD, as shown in FIG. 2(C). Data which constitute the first two bits of the 4-bit output 1 are stored in the data areas R1 and R2 through the scrambler circuit 61, at the timing as shown in FIG. 2(D). Thereafter, in response to the clock "3" two cycles after the cycle at which the head address has been determined, even if an address is not determined from the outside, the scrambler control circuit 10 activates the column select lines in the same way as with the case where the third address of the output 1 has been determined from the outside. FIG. 2(F) shows the status in which the data are read to the data lines DLN and further determined by the read/write data lines RWD. The third and fourth bits of the 4-bit output 1 determined as described above are stored in the data areas R3 and R4 of the data register 52 through the scrambler circuit 62, as shown in FIG. 2(E). The similar operation is repeated in sequence for each two cycles of the clock CLK.

On the other hand, the data stored in the data registers 51 and 52 are accessed in the sequence of the data areas R1, R2, R3 and R4 as shown over the clock CLK in FIG. 2(A). After having been transferred to the read/write data lines RWD, the data are stored in the data registers 51 and 52 in accordance with the address sequence expected by the scrambler control circuit 10. Therefore, it is possible to output the data in the expected sequence. On the other hand, when the head address of a series of the data is determined again, the data can be outputted as the output 2 or the output 3, as shown in FIGS. 2(H) and (I), respectively. In more detail, when data are required to be outputted continuously beginning from a new address in response to the clock CLK "12", a new head address is determined from the outside in response to the clock CLK 9. Then, new data can be transferred in the same way as described above; the data are determined as shown by A in FIG. 2(C); stored in the data areas R1 and R2; and further outputted continuously following the output 1.

Further, before a series of the data of the output 2 are outputted, a new head address of the output 3 is determined. The data of the output 3 are outputted beginning from the data area R3 of the data register 52. The sequence of the data transfer is the same as with the case of the outputs 1 and 2. The new head address is determined at the row of the clock CLK "11". The 4-bit data including the head address are determined on the read/write data lines RWD, as shown by B in FIG. 2(F). The 2 bits of the 4-bit data are selected by the scrambler circuit 62, and stored in the data areas R3 and R4 of the data register 52 at the timing as shown in FIG. 2(E). In the same way, the 4-bit data are transferred for each two cycles, and further 2 bits of the data are selected. The above-mentioned sequence is repeated to output a series of data continuously.

Further, in the case where a series of 8-bit data are outputted, the scrambler control circuit 10 selects the column select lines C1 to Cn/2 and the scrambler circuits 61 and 62, respectively in sequence as follows: Here, the description will be made on condition that the column select lines C1 to C4 shown in FIG. 1 correspond to the data sequence of a series of 8-bit data.

The mode in which 8-bit data are accessed in series circularly will be first explained. In this case, the number of the head address is eight. Table 1 lists the relationship among the eight serial and cyclic access modes classified according to the eight head address, a pair of select lines C1 to C4 to be selected, 2-bit read/write data lines RWD to be selected from the read/write data lines RWD on which the 4-bit data have been determined, and the data areas R1 to R4 of the data registers 51 and 52, respectively.

                  TABLE 1                                                          ______________________________________                                         SER ACCESS SEQ                                                                              (a) R1 R2 R3 R4    R1 R2 R3 R4                                    ______________________________________                                         (1)          (A) (c1,c2)                                                                              (c2,c3)  (c3,c4)                                                                              (c4,c1)                                  1-2-3-4-5-6-7-8                                                                             (B)  1  2  3  4     1  2  3  4                                    (2)          (A) (c1,c2)                                                                              (c2,c3)  (c3,c4)                                                                              (c4,c1)                                  2-3-4-5-6-7-8-1                                                                             (B)  2  3  4  1     2  3  4  1                                    (3)          (A) (c2,c3)                                                                              (c3,c4)  (c4,c1)                                                                              (c1,c2)                                  3-4-5-6-7-8-1-2                                                                             (B)  3  4  1  2     3  4  1  2                                    (4)          (A) (c2,c3)                                                                              (c3,c4)  (c4,c1)                                                                              (c1,c2)                                  4-5-6-7-8-1-2-3                                                                             (B)  4  1  2  3     4  1  2  3                                    (5)          (A) (c3,c4)                                                                              (c4,c1)  (c1,c2)                                                                              (c2,c3)                                  5-6-7-8-1-2-3-4                                                                             (B)  1  2  3  4     1  2  3  4                                    (6)          (A) (c3,c4)                                                                              (c4,c1)  (c1,c2)                                                                              (c2,c3)                                  6-7-8-1-2-3-4-5                                                                             (B)  2  3  4  1     2  3  4  1                                    (7)          (A) (c4,c1)                                                                              (c1,c2)  (c2,c3)                                                                              (c3,c4)                                  7-8-1-2-3-4-5-6                                                                             (B)  3  4  1  2     3  4  1  2                                    (8)          (A) (c4,c1)                                                                              (c1,c2)  (c2,c3)                                                                              (c3,c4)                                  8-1-2-3-4-5-6-7                                                                             (B)  4  1  2  3     4  1  2  3                                    ______________________________________                                          (a): DATA AREAS OF DATA REGISTERS                                              (A): A PAIR OF COLUMN SELECT LINES SELECTED                                    (B): RWD LINES CONNECTED TO REGISTERS                                    

The mode in which 3 address bits representative of the 8-bit series data are accessed by repeating "0" and "1" in sequence irrespective of the carry bit from the least significant bit will be next explained. In this access sequence, the least significant bit repeats "0" and "1" alternately for each cycle; the second bit repeats "0" and "1" for each two cycles as "00110011"; and the third bit repeats "0" or "1" for each four cycles as "0000111100001111". Table 2 lists the similar relationship among the eight serial and cyclic access modes classified according to the eight head address, a pair of select lines C1 to C4 to be selected, 2-bit read/write data lines RWD to be selected from the read/write data lines RWD on which the 4-bit data have been determined, and the data areas R1 to R4 of the data registers 51 and 52, respectively.

                  TABLE 2                                                          ______________________________________                                         SER ACCESS SEQ                                                                              (a) R1 R2 R3 R4    R1 R2 R3 R4                                    ______________________________________                                         (1)          (A) (c1,c2)                                                                              (c2,c3)  (c3,c4)                                                                              (c4,c1)                                  1-2-3-4-5-6-7-8                                                                             (B)  1  2  3  4     1  2  3  4                                    (2)          (A) (c1,c2)                                                                              (c2,c3)  (c3,c4)                                                                              (c4,c1)                                  2-3-4-5-6-7-8-1                                                                             (B)  2  1  4  3     2  1  4  3                                    (3)          (A) (c2,c1)                                                                              (c1,c4)  (c4,c3)                                                                              (c3,c2)                                  3-4-5-6-7-8-1-2                                                                             (B)  3  4  1  2     3  4  1  2                                    (4)          (A) (c2,c1)                                                                              (c1,c4)  (c4,c3)                                                                              (c3,c2)                                  4-5-6-7-8-1-2-3                                                                             (B)  4  3  2  1     4  3  2  1                                    (5)          (A) (c3,c4)                                                                              (c4,c1)  (c1,c2)                                                                              (c2,c3)                                  5-6-7-8-1-2-3-4                                                                             (B)  1  2  3  4     1  2  3  4                                    (6)          (A) (c3,c4)                                                                              (c4,c1)  (c1,c2)                                                                              (c2,c3)                                  6-7-8-1-2-3-4-5                                                                             (B)  2  1  4  3     2  1  4  3                                    (7)          (A) (c4,c3)                                                                              (c3,c2)  (c2,c1)                                                                              (c1,c4)                                  7-8-1-2-3-4-5-6                                                                             (B)  3  4  1  2     3  4  1  2                                    (8)          (A) (c4,c3)                                                                              (c1,c2)  (c2,c3)                                                                              (c3,c4)                                  8-1-2-3-4-5-6-7                                                                             (B)  4  3  2  1     4  3  2  1                                    ______________________________________                                          (a): DATA AREAS OF DATA REGISTERS                                              (A): A PAIR OF COLUMN SELECT LINES SELECTED                                    (B): RWD LINES CONNECTED TO REGISTERS                                    

In Tables 1 and 2, the selection (A) of the column select lines C1 to Cn/2 and the connection (B) of the selected read/write data lines RWD to the data areas R1, R2, R3 and R4 of the data registers 51 and 52 are both shown in the same column from the functional standpoint. However, the operational timings are different from each other. Further, the data selected and transferred through the column select lines C1 to Cn/2 are added thereafter to the data areas R1, R2, R3 and R4, as depicted by the timing chart shown in FIG. 2.

Further, in the above-mentioned embodiment, the number of columns b11 to b(n/2)2 connected to the data lines DLN simultaneously by the column select lines C1 to Cn/2 is two. In the actual system, however, this number changes according to the time required to determined the data beginning from the columns b11 to b(n/2)2 to the read/write data lines RWD.

FIG. 3 shows another embodiment of the semiconductor memory device according to the present invention, which is configured on the basis of the above-mentioned standpoint. In FIG. 3, two sets of the data stored in the columns b11, b23, b13, b21, b22, b23, . . . are selected simultaneously 3 bits by 3 bits through the column select lines C1, C2, . . . by the column gates 11, 12, 13, . . . Therefore, the number of the data lines DLN and that of the read/write data lines RWD are six, respectively. Further, the number of bits of the data register 51 becomes 3 bits in correspondence to the data areas R1, R2 and R3, and similarly the number of bits of the data register 52 becomes 3 bits in correspondence to the data areas R4, R5 and R6.

As described above, in the configuration as shown in FIG. 3, two sets of the columns b11, b12 and b13; the columns b31, b32 and b33; the columns b41, 42 and 43 are selected simultaneously by the column gates 11, 12 and 13, and then outputted to the data lines DLN as 6-bit data. The outputted 6-bit data are transferred to the read/write data lines RWD through the data buffer 4, and further transferred to and stored in the data registers 51 and 52 3 bits by 3 bits through the scrambler circuits 61 and 62, respectively. The stored data can be outputted to the outside through the data buffer 8 by selecting the data areas R1, R2, R3, R4, R5 and R6 of the data registers 51 and 52 through the data selection section 9. In this embodiment, the addresses are updated for each 3 cycles.

In general, when the data are transferred from the columns to just before the registers within a (a indicates an integer) cycles, the number of the columns selected by one column select line is equal to "a". Therefore, when two column select lines are selected simultaneously, 2 "a"-bit data can be transferred. Here, although the number of output registers is 2"a", the data are selectively stored in the "a"-unit registers by selecting "a"-bit data from the 2 "a"-bit data. As described above, it is possible to access a series of data more than the number of the output registers by selecting the two column select lines for each "a" cycles.

As describe above, according to the semiconductor memory device of the present invention, in the synchronous system such that the data are transferred from the columns of the memory cell array to the output registers during a basic data transfer time of "a" cycles of the basic clock, the operation is as follows: data are transferred from the columns of "a" bits simultaneously by selecting one column select line. In transferring data for each "a" cycles, 2 "a" bit data are transferred by selecting two column select lines. As described above, "a"-bit data are stored selectively in the "a"-unit output registers of the 2 "a"-unit output registers. Accordingly, since "a"-bit data exist always in the 2 "a"-bit data transferred from any given address, it is possible to store data in the "a"-unit registers in a predetermined data access sequence for each "a" cycles. In other words, a new head address can be set for each "a" cycles and further a series of data can be accessed continuously, irrespective of the number of the data transfer lines and the data registers, thus enabling an optimum synchronous data access.

As described above, in the semiconductor memory device according to the present invention, column data more than the number of the data registers arranged on the output side can be accessed continuously, irrespective of the number of the data registers, and further any access start address can be determined. 

What is claimed is:
 1. A semiconductor memory device, comprising:a memory cell array (MCA) composed of a plurality of memory cells arranged in a matrix pattern having a plurality of columns, 2 "a"-units of the columns being selectable simultaneously; data register means composed of two "a"-bit registers each having "a"-units of single-bit registers; control means for selecting 2 "a"-units of the columns once every "a"-cycles of a clock inputted externally, selecting "a"units of data from data of the 2 "a"-units of the columns selected in first "a"-cycles, storing "a"-units of the selected data in a first of the two "a"-bit registers in a sequence of read addresses, selecting "a"-units of data from data of the 2 "a"-units of the columns selected in succeeding "a"-cycles, and storing "a"-units of the selected data in a second of the two "a"-bit registers in the sequence of read addresses; and data output means for outputting 2 "a"-units of the data stored in said data register means by scanning the single-bit registers constituting said register means in a constant sequence, irrespective of the sequence of the read addresses.
 2. The semiconductor memory device of claim 1, wherein said data output means outputs data in synchronism with the clock (CLK) inputted externally.
 3. The semiconductor memory device of claim 2, wherein the plurality of the columns are composed of column groups fixedly combined for every "a"-units such that "a"-units of the fixed combination is selected simultaneously, thereby selecting 2 "a"-units of the columns of the two "a"-unit combinations.
 4. The semiconductor memory device of claim 3, wherein said control means comprises a plurality of column select lines, each for selecting one of said column groups.
 5. The semiconductor memory device of claim 4, wherein the columns are connected to the single-bit registers, respectively, through a data transfer line.
 6. The semiconductor memory device of claim 5, wherein the data transfer line includes 2 "a"-units of data transfer lines each composed of at least a single line for transmitting two complementary signals.
 7. The semiconductor memory device of claim 6, wherein said control means executes a first control operation such that in response to a head address in the sequence of read addresses, a column select line for selecting the column group containing a head address column and a column select line for selecting the column group containing an address column of a subsequent address after the head address is selected simultaneously.
 8. The semiconductor memory device of claim 7, wherein said control means executes a second control operation such that the head address can be set externally in the sequence of the read addresses for each of the "a"-cycles of the clock outputted externally;"a"-units of data are selected from data of 2 "a"-units of columns selected in first "a"-cycles, the selected data being stored in the first of the two "a"-bit registers in the sequence of the read addresses; and "a"-units of data are selected from data of the 2 "a"-units of the columns selected in succeeding "a"-cycles, the selected data being stored in the second of the two "a"-bit registers in the sequence of the read addresses.
 9. The semiconductor memory device of claim 8, wherein scramblers are connected between the data transfer lines and the first and second registers, respectively, and said control means executes the second control operation by controlling the scramblers, respectively.
 10. The semiconductor memory device of claim 8, wherein "a" is equal to
 2. 11. The semiconductor memory device of claim 8, wherein "a" is equal to
 3. 12. The semiconductor memory device of claim 7, wherein "a" is equal to
 2. 13. The semiconductor memory device of claim 7, wherein "a" is equal to
 3. 14. The semiconductor memory device of claim 2, wherein "a" Is equal to
 2. 15. The semiconductor memory device of claim 2, wherein "a" is equal to
 3. 16. The semiconductor memory device of claim 1, wherein "a" is equal to
 2. 17. The semiconductor memory device of claim 2, wherein "a" is equal to
 3. 